Flat panel displays such as liquid crystal displays and organic EL displays have interlayer insulating films to insulate wiring layers from each other. The interlayer insulating films need to be formed with hole patterns for electrical connection of the wiring layers while ensuring insulation between the wiring layers. For this reason, the interlayer insulating films are generally made of positive photosensitive materials. As typical positive photoresist materials, there are used compositions in which quinone diazide compounds are added to acrylic resins (see Patent Documents 1 and 2).
In recent years, flat panel displays are often configured as touch panel type displays. In order to improve the transparency and functionality of these flat panel displays, it becomes necessary to perform heat treatment and film forming operation at higher temperatures for the formation of transparent electrodes such as ITO with high transparency and high conductivity. Accordingly, protective films or insulating films for the transparent electrodes need to have heat resistance during high-temperature processing. Acrylic resins are however not sufficient in heat resistance and can cause deterioration in transparency by coloring or deterioration in electrode conductivity by degassing during high-temperature substrate treatment and transparent electrode film forming operation.
On the other hand, polysiloxane compounds are known to have both high heat resistance and high transparency. There are used positive photosensitive resin compositions in which quinone diazide compounds are added to polysiloxane compounds (see Patent Document 3). These materials are high in heat resistance and cause less deterioration in transparency even during high-temperature substrate treatment, thereby being able to form high-transparency films, but are low in alkaline developer solubility and developability. It has thus been increasingly demanded to provide polysiloxane compounds with sufficient alkali developability for fine processing by light exposure. Patent Document 4 discloses, as a component of a positive resist composition for the formation of a high-resolution resist pattern, a polysiloxane compound having introduced therein an acidic group such as phenol group or carboxyl group to impart alkali solubility required for development.
As mentioned above, the introduction of acidic groups such as phenol groups, carboxyl groups, silanol groups and fluorocarbinol groups is an effective technique for imparting alkali solubility to the polysiloxane compounds. For example, there are known positive photosensitive resin compositions containing polysiloxane compounds with phenolic hydroxy groups or carboxyl groups in combination with photoacid generators or quinone diazide compounds (see Patent Documents 5 to 8). These polysiloxane compounds, when used as components of the compositions, exhibit alkaline developer solubility and developability but face problems of low transparency and coloring under high-temperature conditions due to the presence of the phenolic hydroxy group or carboxy groups. In the case of forming films using polysiloxane compounds with silanol groups, there arises a problem with the physical properties of the films due to the occurrence of water elimination or cracking by film loss or condensation reaction when the amounts of silanol groups in the polysiloxane molecules are large. When the amounts of silanol groups in the polysiloxane molecules are small, by contrast, the polysiloxane compounds cannot exhibit sufficient alkali solubility.
From the above, it is known that fluorocarbinol groups are effective in imparting alkali solubility to the polysiloxane compounds without causing loss of transparency and film-forming properties. Among others, a hexafluoroisopropanol group (2-hydroxy-1,1,1,3,3,3-hexafluoroisopropyl group: C(CF3)2OH group) is particularly effective. Patent Document 9 discloses that a polysiloxane compound to which a hexafluoroisopropanol group is introduced via a straight, branched or cyclic aliphatic hydrocarbon group is useful as a component of an alkali developable composition. In this polysiloxane compound, the aliphatic hydrocarbon group is formed by hydrosilylation such that the hexafluoroisopropanol group is bonded to a silicon atom via the aliphatic hydrocarbon group. However, such an aliphatic hydrocarbon moiety is thermally decomposed under high-temperature conditions. This polysiloxane compound is thus not sufficient in heat resistance.